It is well known that silver particles are used as bactericide and antiviral agents, and its function as a bactericide increases in a proportional inverse relation to the size of the particle, for that reason the nanoparticles are of special interest. This material also has applications in catalytic hydrogenization of organic compounds, among others.
To avoid confusion in the use of certain terms herein, “nanoparticle” is generally used to refer to particles that have a diameter equal to, or less than 100 nm; “monodispersion” is used to identify the particles with low variability in size, and “stability” is understood as the quality that the material has in not changing the size of the particles and monodispersion without applying mechanical or chemical means during the storage period.
In the prior art, there are known two types of processes for the fabrication of nanoparticles of metallic silver:
a) plasma via, where a rod of metallic silver is heated to vaporization, then the vaporized silver is cooled in a suitable atmosphere, obtaining a fine dust of metallic silver, (in an inert atmosphere) or a compound of silver associated to the nature of the atmosphere used.
b) wet reduction via, where a silver ion solution is submitted to a process of reduction, in the presence of surfactants and stabilizers to control the size of the product.
Recently there have been reports on the effect of the presence of light in applications for the reduction of silver by wet reduction (“Preparation of silver nanoparticles by photo-reduction for surface-enhanced Raman scattering”; Huiying Jia, Jiangbo Zeng, Wei Song, Jing An, Bing Zhao; Thin Solid Films 496 (2006) 281-287. “Photochemical preparation of nanoparticles of Ag in aqueous solution and on the surface of mesoporous silica”; G. V. Krylova, A. M. Eremenko, N. P. Smirnova, S. Eustis; Theoretical and experimental chemistry (2005) 41(2) 105-110), where the addition of surfactants and stabilizers is not necessary, since the metallic silver particles form on the surface of a substrate; the reaction lasts up to 3 hours.
Xuelin (“Seedless, surfactantless photoreduction synthesis of silver nanoplates”; Xuelin Tian, Kai Chen, Gengyu Cao; Materials Letters 60 (2006) 828-830) reports the use of sodium citrate as the reducing agent to obtain silver nanoparticles in the presence of light.
In other articles, the precipitation of metallic silver nanoparticles is mentioned, where the reaction can last from 8 to 24 hours (CN1810422, Gao, 2006). In other publications to accelerate the reaction, the mixture is heated to temperatures close to 100° C. (CN1686646, Liu, 2005; CN1669914, Luo, 2005).
It is clear that in the case of wet reduction processes, a significant problem exists in the selection of additives since they should be compatible between the surfactant used in the reaction and the application for which the nanoparticles are destined, or on the contrary, submit the product to a process to eliminate the surfactant; furthermore, the concentration of the additive in the reaction mixture needs to be controlled to influence the size of the silver nanoparticles; on the other hand, it is important to point out that the reaction times are relatively long, such that there is a wide variety in the distribution of particle size.